The present invention relates to a mobile IP network system having an address allocation management function of dynamically allocating an address to a mobile node in accordance with the mobile Internet Protocol (mobile IP).
There have increased over the recent years communication modes of utilizing handheld information terminals such as PDAs (Personal Digital Assistants), notebook type personal computers and so on as communication terminals and connecting these terminals to the IP network from a variety of places different from those usual.
The present Internet Protocol technology and mobile IP (strictly, mobile IPv4) technology enable mobility transparent communications to be actualized in a mobile IP network system, wherein a node connected normally to specified network (that may be called a home network as a base network to a mobile target node (mobile communication terminal)) is temporarily connected as a mobile node to a different network (a foreign network utilized in a local area to which the mobile node moves), and receives an IP packet originally addressed (transmitted) to a fixed IP address (home address) of this mobile node from a sender node in the home network, and namely the IP packets are forwarded to anywhere the mobile node moves to.
A method of allocating the IP address fixedly to the mobile node concerned and a method of temporarily allocating (leasing) IP address on the basis of DHCP (Dynamic Host Configuration Protocol) are provided as methods of allocating the IP address as a home address to the mobile node.
According to this DHCP, a DHCP server batchwise manages the IP addresses. For example, if the mobile node as an information device is newly connected to the home network and operated, this information device functions as a DHCP client (client terminal).
The DHCP client normally connected to the home network broadcasts an IP address allocation requests to the DHCP server on the home network immediately after the DHCP client has been operated. The DHCP server detecting this IP address allocation request provides the DHCP client with an IP address that can be allocated at that point of time.
In the case of the mobile node, this mobile node, when accessing the home network via the foreign network, sends a registration request to the home agent. If the IP address (home address) of the mobile node is not yet set at this registration request time, it is a rule that the home agent as a proxy of the mobile node obtains the IP address from the DHCP server and notifies the mobile node connected to the foreign network of this obtained IP address. It does not happen that the mobile node requests directly the DHCP server to allocate the IP address.
An up-to-date and popular way of utilizing the mobile node is that the user of the mobile node establishes a contract with a provider such as ISP (Internet Service Provider) for providing a certain category of information communication service and receives this service.
The number of the mobile nodes (contract user count) receiving this service is larger than the number of the IP address held by the provider, and it is therefore impossible for all the mobile nodes to receive the services at the same timing. Consequently, there appear the users who desire to use the mobile nodes any time in a way that corresponds to a content of the contract.
Further, if a registration request is given from the mobile node, the DHCP server must allocate the IP address to the mobile node. When used as by an e-mail and if accessed from a multiplicity of mobile nodes all day though short in time, the DHCP server allocates the IP address each time, a rise in load upon the home network is inevitable.
According to the conventional mobile IP network system, if the mobile node is unable to obtain the IP address from the DHCP server, or if unable to obtain the IP address from a reserve pool held by the home agent, the mobile node cannot be provided with the mobility transparent communication service.
FIGS. 21(A) and 21(B) show an outline of a process for dynamically allocating the IP address to the mobile node in the conventional mobile IP network system.
The conventional mobile IP network system, though an illustration of this system architecture is herein omitted, includes a home network system and a foreign network system. The home network system is connected to the foreign network system via an IP (IPv4) network such as the Internet or Intranet.
The home network system is configured by a home network, a home agent connected to this home network and serving to administer a connection from the foreign network, and a general terminal (a mobile node as a mobile target).
Further, the foreign network system is configured by a foreign network, a mobile node connected to the foreign network, making a request for an access to the home network and forwarding/receiving IP packets, and a foreign agent that administers a connection to the home network from the mobile node via the foreign network.
The home agent in the home network system has an address allocation management function of dynamically allocating the IP address (home address) to a device connected afresh via the foreign network.
As indicated by processing steps SA01 to SA05 shown in FIG. 21(A) and processing steps SB01 to SB05 shown in FIG. 21(B), when the home agent receives a new registration request from the mobile node connected to the foreign network via the foreign agent, the home agent, based on the address allocation management function, obtains an IP address to be temporarily allocated to the mobile node out of the DHCP server or a reserve pool, and continues the registration process for the mobile node with the IP address obtained.
The home agent, if unable to obtain the IP address to be temporarily allocated to the mobile node out of the DHCP server or the reserve pool, sends to the mobile node a reply that the address cannot be obtained. Herein, the DHCP server is normally connected to the home network, and the reserve pool is configured on a memory of the home agent.
Note that if the home agent dynamically allocates the IP address to the mobile node, a method of obtaining a free address from the DHCP server or the reserve pool maybe used in combination.
An address allocation to a specified user (who desires for an ever-use of the mobile node) corresponding to the mobile node can be attained by fixing the IP address to the specified user or reserving beforehand the IP address presumed to be necessary in consideration of a node activity ratio by the specified user and allocating the reserved IP address to the specified user.
The number of the addresses usable for the mobile nodes is, however, a finite number, and it follows that the addresses left after allocating the IP addresses to the specified users are allocated to general users corresponding to the mobile nodes. Hence, the number of the general users allowed to receive the services is limited.
Further, queries of the DHCP server for obtaining the IP addresses lead to a traffic load on the home network.